One of the primary factors affecting the unequal heating of the Earth’s atmosphere is latitude. Latitude is the measurement of the distance of a location on the Earth from the equator. The further away from the equator that a location resides, the less sunlight that this location receives.

Why do location at higher latitudes receive less sunlight?

It all has to do with the shape of the Earth. Because the Earth is round, only the front most portion receives direct sunlight. If we pretend that the Earth is a man with a fat round tummy, it is easier to understand why this is the case. Suppose that the man falls asleep in the grass after enjoying reading a book. As he sleeps, a colony of ants climbs onto his stomach. Some of the ants are on the very top of his belly, while others are on either side.

The ants crawling on the top of the man’s stomach are in the direct light of the Sun. The further down the ants climb on either side, the less sunlight there is that can reach the ants. The sunlight becomes more and more spread out.

Now, let's consider another example. This time, instead of light, we will consider shadows. If you go into a dark room and hold a flash light directly behind your hand what will you see? You should see a dark shadow cast on the floor or wall. Now what happens as you move the flashlight up and down with respect to your hand? Your hand’s shadow should become larger and smaller. Notice that the larger your shadow becomes the lighter it becomes, while a shadow cast by light that is directly behind your hand is darker.

The same is true with the light and energy from our Sun. The more direct the light is, the more intense it is, while less direct light is less intense. The angle at which light strikes the surface of the Earth is known as the angle of incidence.